[daip] ACCOR question

[Leonia Kogan]

Michael Bietenholz wrote:
>> Your result looks very strange for me. ACCOR does not do anything 
>> different but averaging the autocorrelation during the given SOLINT 
>> and record the result into the new created SN table.
>> The averaging is provided taking into account the weights.
>> So the average result may be changed when you exclude some visibilities.
> 
> Ooops - sorry for wasting your time.  It turned out that I had made a
> mistake and not UVCOPied all the channels, which caused the
> discrepancy in the ACCOR results.
> 
> It does suggest that the ACCOR results are actually channel-dependent -
> is that expected?
Yes ACCOR averages the frequency channels to go from FX correlator to XF 
correlator. The averaging leads to the auto correlation function at zero 
delay, and all theory of digital correction is considered at the
(cross) (auto) correlation.

Thanks Leonia


> 
>            cheers,      michael
> 
> 
>>>  I've just noticed something a little odd with some results from ACCOR.
>>>  I ran ACCOR as normal on a VLBI data set (continuum; L-band; VLBA +
>>>  GBT + EB; new correlator; 31DEC11 AIPS)
>>>
>>>  I got SN table amplitude corrections near mostly between 0.8 and 1.2,
>>>  as expected.
>>>
>>>  Then I ran UVCOP to loose any visibilities with weights <0.3 (UVCOPPRM
>>>  0 0 0 0 0.3 0: keep autocorrelations).  Only a small fraction of the
>>>  total number of visibilities (0.07%) were lost.
>>>
>>>  I would have expected that ACCOR, when run on this slightly smaller
>>>  UVCOP'ied data set, would return almost the same answer (since we've
>>>  only very slightly changed the visibility data set its working with).
>>>  I found, however, that there are quite systematic differences in the
>>>  ACCOR solutions, which are now about a few % lower (the before/after
>>>  UVCOP amplitude difference is quite consistent througout the run).